This is Part 4 in a series called “Why RCTs?” which explores experiences with and without the benefit of randomized study across disciplines. This installment takes on a gadget most are familiar with, and one that is currently all the rage. What can we learn from new data that challenge our previous understanding of the relationship between technology and our behavior?

Many Americans use Fitbits and similar activity trackers as health aids, and sometimes even as fashion accessories. Some have become mildly obsessed with checking the app repeatedly during the day to see the “count” of steps or stairs approach or even pass their goals. Activity trackers could make us feel as if we are getting enough exercise during our busy days without having to hit the gym. They could encourage us to walk home or to forgo the elevator. Even better than Pokémon-GO!

But if these devices help us get more exercise, then we would also expect them to help us lose weight, right? It’s an encouraging thought that jumps on trends of the decade: personal accountability, healthy living, self-growth, tech, adaptability and busy schedules. It turns out, though, that we shouldn’t be so quick to assume their effectiveness, and recent data suggests otherwise.